MAKHACHKALA, Russia — The parents of the two Boston Marathon bombing suspects say American investigators have once again come to their home in the southern Russian province of Dagestan to talk to them about their elder son.

Tamerlan Tsarnaev spent six months in Dagestan last year, and investigators have been trying to determine whether he was influenced or trained by local Islamic militants.

His mother, Zubeidat Tsarnaeva, told The Associated Press that the Americans questioned her and her ex-husband on Wednesday and Thursday. She said the questions have remained focused on who could have influenced their son in Russia.

Tamerlan Tsarnaev was killed in a police shootout days after the April 15 attack, and his brother was injured. Later that month, a team of U.S. investigators traveled to Dagestan to question both parents.